isless() for nullable vs non-nullable

Author: alyst

src/operators.jl

@@ -158,3 +158,29 @@ if !method_exists(isless, Tuple{Nullable{Int}, Nullable{Int}})
     isless(x::Nullable{Union{}}, y::Nullable) = false
     isless(x::Nullable, y::Nullable{Union{}}) = !isnull(x)
 end
+
+function isless{S,T}(x::Nullable{S}, y::T)
+    # NULL values are sorted last
+    if null_safe_op(@functorize(isless), S, T)
+        (!x.isnull && isless(x.value, y))
+    else
+        if x.isnull
+            return false
+        else
+            return isless(x.value, y)
+        end
+    end
+end
+
+function isless{S,T}(x::S, y::Nullable{T})
+    # NULL values are sorted last
+    if null_safe_op(@functorize(isless), S, T)
+        y.isnull || (!y.isnull && isless(x, y.value))
+    else
+        if y.isnull
+            return true
+        else
+            return isless(x, y.value)
+        end
+    end
+end